1. Field of the Invention
This invention relates generally to apparatus and method used for ion implant dose and energy measurement. Particularly, this invention relates to a novel apparatus and method to perform a more accurate implant dose and/or energy measurement by applying a reflective measurement technique implemented with an optically dose-sensitive layer with measurements scaled to a referenced reflection without the dose-sensitive layer.
2. Description of the Prior Art
Precise measurement of dose and/or energy of ion implantation has become a challenge to those of ordinary skill in the art of integrated circuit (IC) manufacture. Particularly, as smaller and denser device geometry on integrated circuit (IC) chips are now built by the microelectronics industry for achieving increasing amounts of computing power. Specifically, the advent of denser, larger-scale integration has placed greater demand on the precise dopant concentration and uniform distribution. For example, as the circuit density has increased, designers have used lower operating voltages for complex circuits such as microprocessors in order to limit power dissipation and operating temperatures. The lower operating voltages requires more precision in the CMOS transistor switching threshold voltage (Vt). Ion implantation is now used for precisely setting the threshold voltage Vt. Limitations and difficulties to precisely measure the dose and energy of ion implantation at low dose levels would also cause limitations to further miniaturize and limit the manufacturing yields of high performance integrated circuits.
Referring to FIGS. 1A to 1C for a transmission technique applied to measure the dose and/or energy of an ion implantation. FIG. 1A shows a beam of light emitted from a light source project to a light detector that is focused to a small area in the beam path. FIG. 1B shows a film inserted at the focal point in the beam path. The light intensity is reduced with the film inserted at the focal point. Measurement of the light intensity at multiple points of the thin film is employed to develop a map of ion implant dose. At each point, the optical density of the film is determined by taking the logarithm of the ratio of the light intensity without the film to the light intensity with the film. As that shown in FIG. 1C, the film is supported on a glass or quartz substrate that is ground to a shape of a wafer normally used by the ion implanter for IC production. The light beam intensities at multiple points are measured before and after the ion implantation. The optical density changes are determined at each measurement site and a comparison is made with the known density changes from known implantation doses at specific energies or known energies at specific doses to determine the dose or energy of implantation for each measurement site.
The transmission measurement technique employed in the prior art method has a disadvantage due to requirement of using a transparent substrate. Possible contamination or damages of the transparent substrate can cause measurement errors. In the case when a glass substrate is broken, major expenses, manpower and loss of equipment productivity must be involved to remove the broken pieces. Since the ion implanter and all the associated machines are set up to handle silicon substrate, the use of glass or quartz substrates adds to the complexities of the material handling processes.
Therefore, a need still exists in the art of semiconductor industries to provide novel and improved apparatus and method for ion implant dose and energy measurements to overcome the limitations and difficulties now faced by those of ordinary skill in the art. It is desirable that the measurement techniques are compatible with the standard manufacture processes of integrated circuit such that minimum disruptions and adverse impacts would arise from using these novel measurement procedures. It is further desirable that the apparatus and sample substrate used for dose and energy measurements can be employed with ion beams provided from the implanter within the regular range of IC device manufacture. Further adjustment of the implanter energy and dose rate is not required and better measurement precision can also be achieved when ions beams of same range of energies, same dose rate and same implanting times are applied for production implantation and for implantation dose measurements.